The temporal expression of various biological rsponses was determined in Bluegill SunfishLepomis macrochirus exposed under controlled laboratory conditions to sediment containing high concentrations of polynuclear aromatic hydrocarbons, polychlorinated biphenyls and heavy metals. Liver, gill, blood, kidney, brain, spleen and intestine were removed from Sunfish sampled at 1, 2, 4, 8, 16, and 40 weeks post-exposure. Biomarker data were recorded for specific proteins, enzymatic activities, DNA integrity, and histopathology. Biomarkers in the laboratory exposed fish were similar to those of indigenous Sunfish sampled from the site of origin of the contaminated sediment. Several patterns of development of biomarkers over time were also evident. For example, the responses of certain biomarkers are not time-dependent (i.e., intestine and gill ATPase activities) while that of others, such as brain ATPase activity, liver cytochrome P450 and NADPH content, stress proteins, chromatin proteins and DNA strand breaks, fluctuate over time. Still other biomarkers, such as EROD activity, zinc protoporphyrin content of the blood, and DNA adducts, showed marked increases over time. Such patterns need to be considered when comparing laboratory and field results and deciding which biomarkers to use for biomonitoring programs. Implications for natural selection and population/community level responses are also discussed.